Evidence for Evolution

Evidence for Evolution

1. Paleontology

   • Paleontology is the scientific study of prehistoric life in general. Paleontologist’s utilize fossils to show change in species and to understand how they have evolved from a common ancestor or morphed over time, supporting the theory of evolution.
     • Tiktaalik Roseae
       • Also known as, “Fishapod”, is a 375 million year old fossil fish that was discovered Ellesmere, Nunavut, Canada in 2004. Tiktaalik has a combination of fish and amphibian traits. It is known to be a transitional species between the primitive fish and first tetrapods, four - legged animals. This provides evidence that the hind legs are actually an evolution from hind fins.
     • Evolution of horses
       • The evolution of horses is widely studied by paleontologists, primarily by analyzing the change in their legs and their teeth over time.
         • Hyracotherium are cousin species of horses, their forelimb consists of four toes and are much smaller compared to modern horses. They had small teeth, thus, they ate leaves. They are the oldest discovered species out of the following horses.
         • Mesohippus/Miohippus are larger than Hyracotherium, however, their forelimb consists of three toes. Their teeth were bigger than Hyracotherium, though, they still ate leaves.
         • Merychippus are larger than Mesohippus/Miohippus and their middle toe developed into a hoof that did not have a pad the the bottom. Their teeth were larger than their ancestors, and now they started to eat grass.
         • Pliohippus are considered to be ancestors of present day horses. Their size and shape were similar to those of the modern horse, however their teeth were curved.
         • Equus is a category that consists of modern day horses, zebras and donkeys. Equus' are larger than their ancestors and have bigger and straighter teeth to eat grass. Equus; have a large central toe and their side toes are vestigal structures, previously used by Mesohippus/Miohippus and Merychippus.
     • Anchiornis
       • Anchiornis was a four-winged birdlike species that lived approximately 160 million years ago. Anchiornis was an early member of the group, Avialae, however, it was also closely related troodontid dinosaurs. Anchiornis was roughly 14 inches long and had long feathers and small bushy plumes behind its necks, thought to be used for insulation and water-repulsion. The specie are thought to have glided down trees and was highly unlikely to be capable of powered flights. This transitional fossil provided evidence relating primitive birds to dinosaurs and also how the birds moved before the were able to fly. Similar to modern birds, Anchiornis exhibited a complex pattern of coloration, and by comparing modern birds to these ancient species, the evolution of feathers as well as the wings can be noticed.

2. Biogeography

   • Biogeography is the study of the distribution of different species throughout the world, and how they ended up in the locations they are found in. The study also analyzes the characteristics of organisms to their respective environment and to those similar around the globe. Through this study, biogeographists speculated that organisms once lived together on Pangaea a super-continent, however, once Pangaea split the organisms were separated and developed differently in response to their environments around the world.
     • Marsupials
       • Marsupials are a group of organisms characterized by premature birth and continued development in a pouch attached to the nipples on a mother’s lower belly. These mammals are commonly found in Australia and New Zealand, however, many species can also be found thousands of miles away on the continents of South America and North America. This provides evidence that when the continents were united, original Marsupial species existed however when the continents separated, the marsupials evolved independently to adapt to their different environments.
     • Glossopteris
     • Cynognathus
     • Mesosaurus
     • Lystrosaurus
     • Image showing the migration of the following species: Glossopteris (in green), Mesosaurus (in blue), Cynognathus (in orange) and Lystrosaurus (in red), during Pangaea
     • Biogeographical evidence for evolution can be observed by analyzing the location and distribution of the fossils of the following species: Glossopteris, Mesosaurus, Cynognathus and Lystrosaurus. The fossils for these species were discovered in various locations around the world, specifically those that were closely related during Pangaea. Pangaea is theorized to be a super-continent that millions of years ago united all the continents present in the modern day world. The fossils for the species were found in different places, including: South America, Antarctica, Australia, South Africa and India. The distribution of fossils across these nations support the theory of Pangaea as species such as Lystrosaurus and Cynognathus are male dominant species, making it impossible for them to get across the oceans.

3. Morphology / Anatomy

   • Comparative anatomy or morphology is the study of body structures of different organisms to understand the changes that have undergone in response to their respective environment.
     • Homologous Structures
       • Homologous structures, are body parts of organisms with similar structure showing commonalities that have been derived from a common ancestor, although, the body parts may have different functions.
         • The image on the right provides examples of the forelimb in six vertebrates from 6 different species. The common structure of the forelimb is theorized by scientists to arise through evolution from a common ancestor. Although the structures contain similar component, the function of the structure may not be the same. For example, the bat's wings and dolphin's flippers originate from early mammalian ancestors, however, they perform very different tasks of flying and swimming respectively.
     • Analogous Structures
       • Analogous structures, are structures with similarities between organisms in an ecosystems, however, they evolved independently, thus, they do not share a common ancestor.
         • Penguins & Fishes
           • An example of an analogous trait is fins. Penguins and fish are two aquatic animals which utilize their fin-like structures to navigate through water. However, penguins are considered birds due to their bird-like characteristics making them drastically different than fish. This provides evidence where a structure evolved in very different species in order to adapt to their environment, and not common ancestry.
     • Vestigial Structures
       • Vestigial structures are bones or structures in a species which serve no purpose for the specie, but are believed to be of use before evolution.
         • The Blind Fish Astyanax Mexicanus
           • The species of fish known as Astyanax mexicanus, dwell in caves deep underground off the coast of Mexico. These species cannot see. The pale fish has eyes as it is developing in the egg, however, the eyes begin to degenerate and when the fish are born, their eyes are covered by a flap of skin making them blind. These blind eyes are considered vestigial structures and probably have formed due to living in the darkness for a very long time. An experiment was conducted on these blind fish to determine if their eyes could function in an environment full of light. Scientists removed the lens from from the eyes of a fish dwelling near the surface and implanted it into the eye of the blind fish. An observation was made within eight days that the implanted eyes in the blind fish were starting to develop and in two months, it was a perfectly functioning eye. This proves that through evolution, the eyes of the Astyanax Mexicanus species became vestige to adapt to its dark environment.
     • Embryology
       • Embryology is the study of the formation and development of embryo as well as the fetus.
         • The embryos in the image above, are all from different species. Shockingly, the embryos share similar characteristics. For example, all of the embryos above have gill pouches and also a tail-like structure. These similarities imply of a common ancestor, and that these organisms start out the same before evolving into their unique physical characteristics.
     • Convergent Evolution
       • Convergent evolution is the process in which organisms inside an ecosystem independently evolve similar traits as they adapt to their environments.
         • Bats and Dolphins
           • Bats and dolphins both use echolocation in their respective environments as a method of specialized hunting. It was discovered by scientists that both animals had the same mutation on a particular protein called, prestin, which affects the sensitivity of hearing. Evolutionary biologists compared the bat sequence to other echolocaters primarily focusing on the 2300 genes that exist in single copies, and evaluated how similar each gene was to its counterparts. They discovered that 200 genes had independently changed in a similar manner in echolocaters. THIS IS ALSO ASSOCIATED WITH MOLECULAR EVOLTION

4. Biochemical / Molecular

   • Biochemical evolution or molecular evolution can either be similarities or differences that occur at the molecular level, including: gene sequences, proteins or DNA, between organisms over a period of time.
     • Cetacean & Hippopotamid Artiodactyls
       • A scientific experiment compared the milk protein genes, kappa-casein (exon 4) and beta-casein(exon 7) from cetaceans and other placental mammals. The results of the report suggested that hippopotamid artiodactyls are more closely related to cetaceans that other artiodactyls. This relationship between cetaceans and artiodactyls species implies that some traits of cetaceans were derived from a common ancestor of both, cetacea and artiodactyla.
     • Human & Mouse
       • Despite being radically different in sizes, humans and mice share a lot in common. On average, humans and mice genomes are 85% identical, while other genes can be 99% identical or 60% identical. Due to these similarities in DNA, mice make for a good animals for experimentation for new diseases and therapeutic agents. Mammals that also share a very similar genome to that of humans are CHIMPANZEES
       • 85% genome similarities also hints that mice and humans shared a common ancestor in the past.
     • Cladogram of whales and their closest living relatives
       • The cladogram to the right shows the closest living relatives in terms of DNA sequence to cetaceans: Hippopotamus, ruminant, pig and camel respectively. Based on the information present on the cladogram, it can be noticed that all of these species share a common ancestor and that it was not long ago that hippopotamus and cetacean evolved from a common specie.

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